NC0021156_Pretreatment_HWA_Letter_20190624

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
LINDA CULPEPPER
Director
NORTH CAROLINA
Environmental Quality
June 24, 2019
Via Electronic Mail ([e-mail])
Doug Shoutd
Division Manager of Wastewater
City of Mount Holly
PO Box 406
Mount Holly, NC 28120
Subject: Pretreatment Review of Headworks Analysis (HWA)
City of Mount Holly - NPDES # NCO021156
Gaston County
Dear Mr. Shoutd:
The Pretreatment, Emergency Response, and Collection Systems Unit (PERCS) of the Division of
Water Resources has reviewed the Headworks Analysis (HWA) for the City of Mount Holly. This
HWA was submitted by Suez, the POTW's Pretreatment consultant, and was received by the
Division on March 28, 2019.
The Division concurs with the HWA calculations for all pollutants of concern, with the following
corrections and comments as discussed below. These approved Maximum Allowable Headworks
Loadings (MAHL), Maximum Allowable Industrial Loadings (MAIL), and the basis for these values
are found on the last page of the attached HWA spreadsheet. The results of the HWA are also
listed in the bottom section of the attached Allocation Table. None of the corrections result in
over allocation.
The following corrections were noted during the review of the HWA:
1. Uncontrollable flow: was calculated from the POTW average flow minus total SIU flow
and was updated to 1.18 MGD to match the uncontrollable mass balance spreadsheet.
2. Sludge site area: was updated to 243.2 acres to match the attachment B to the land
application permit.
3. Literature Design values for BOD, TSS and ammonia were used and the design values were
selected for the pass through loading calculations.
Noanacawaur�nD � Q��
North Carolina Department of Environmental Quality Division of Water Resources
512 North Salisbury Street 1 1617 Mail Service Center Raleigh, North Carolina 27699-1617
919.707.9000

4. NPDES limit: for TN was recalculated to 9.16 mg/L. The NPDES permit has a TN limit of
64,200 lb/summer and summer was defined from April 1 to October 31. The
concentration limit was calculated by dividing 64,200 by 7 months by 30 days by 8.34
conversion factor and when by permitted flow 4 MGD.
5. Inhibition concertation: for chromium, lead and nickel were adjusted to reflect the
nitrification inhibition literature values.
6. Uncontrollable concentration: for TSS was updated to 284 mg/L to match the
uncontrollable mass balance spreadsheet.
7. Next HWA Due Date: The HWA was based on 2016-2018 data. Unless conditions at the
POTW change significantly and thus warrant an earlier submittal, the POTW must submit
an updated HWA on or before April 1, 2024. It is likely that the POTW would get a
renewed NPDES permit before this due date. The POTW should notify the PERCS Unit and
have 180 days to update the new NPDES permit limits and apply the dissolved metal
stream standards to the HWA.
Thank you for your continued cooperation with the Pretreatment Program. If you have any
questions or comments, please contact me at [phone] [email: [e-mail]]
or Deborah Gore, Unit Supervisor at [phone] [email: Debora [e-mail]].
vz/mounthoIly_hwa_005
Enclosures: HWA_ AT spreadsheets
Ec with enclosures:
Ms. Nadine Blackwell, Suez
PERCS Unit
Wes Bell, Mooresville Regional Office
Cc without enclosures:
Central Files (Laserfiche)
Sincerely,
DocuSigned by:
Vivien Zhong, PERCS Unit
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